Embedding electrical heaters into exhaust catalysts enhances device performance. Specifically, increasing heater thermal output allows the catalyst temperature to be increased to a point that increases the exhaust efficiency, particularly during periods of low temperature operation. Segmentation of catalyst substrates into zonal regions further provides for targeted heating in the one or more zones. However, previous zonal heating systems employ embedded heaters that rely on radiative and conductive thermal transfer based on heater placement within the catalyst, which may correspond to the zonal regions of the catalyst.
For example, U.S. Pat. No. 7,886,529 discloses a catalyst with multiple bricks arranged in series with a heating element positioned therebetween. U.S. Pat. No. 8,826,647 alternatively discloses a particulate filter segmented into two zones where the electric heater is embedded within the filter. US 2014/0157982 further describes a particulate filter having five zones that can be selectively heated using an electrical heater. Therein, four zones are arranged annularly around a central region while the current is selectively controlled to adjust the heater output within the various zones. With this arrangement, the thermal output in a particular region may depend on managing the zonal heat output based on balancing the energy supply in a region to increase the temperature of the region targeted, and preventing an adjacent or region proximate to the targeted region from also being heated by diffusive heat that spills over into these regions, which may affect a thermal efficiency therein. In this way, control of exhaust heating may become very difficult, particularly in systems with smaller dimensions where available spacing constraint limits the size of the exhaust catalyst.
The inventors have recognized the above-identified, as well as other, issues with such approaches and herein describe exhaust aftertreatment systems and methods for reducing emissions. In particular, an example exhaust gas aftertreatment system described comprises a first catalyst downstream of a branchpoint in a first exhaust pathway, a second catalyst downstream of the branchpoint in a second exhaust pathway, an electrical heater positioned upstream of the branchpoint for heating an exhaust flow, a control unit for adjusting current of the electrical heater, and a valve for adjusting a distribution of exhaust flow to the first and second catalyst, the control unit including instructions to adjust the valve responsive to a substrate temperature within one or more of the first and second catalysts. In this way, the technical result is achieved that an exhaust system may be operated at a higher efficiency across the range of operating temperatures while reducing emissions output from the exhaust system.
Methods for treating exhaust gases are also disclosed. For example, a method is described that comprises electrically heating the exhaust gas, separately determining a temperature differential across two catalysts, actuating a first valve to control an exhaust flow to a first catalyst via a first exhaust pathway, actuating a second valve to control an exhaust flow to a second catalyst via a second exhaust pathway, and differentially heating each of the first and second catalysts using the exhaust flows to the two catalysts. With this arrangement, the combination of valve adjustments and heater output provides for differential control of the electrically heated exhaust flow to each catalyst based on the prevailing conditions within the exhaust, the exhaust flow to each catalyst providing for differential control of a substrate temperature within each catalyst. Inclusion of separate catalysts advantageously allows for different target temperatures to be selected for each catalyst based on a substrate composition therein (e.g., copper vs. iron) to increase the overall efficiency of exhaust operation, which reduces an emission level. In addition, because the first catalyst may reduce emissions more efficiently at a lower temperature compared to the second catalyst that reduces emissions more efficiently at a higher temperature, the methods further comprise adjusting the extent of exhaust flow to each catalyst as a function of temperature. For example, adjustments may increase the exhaust flow to the first catalyst and reduce exhaust flow to the second catalyst in response to a decreasing temperature, whereas adjustments may decrease exhaust flow to the first catalyst and increase exhaust flow to the second catalyst in response to an increasing temperature. Differential control of the exhaust flow in combination with an upstream electrical heater thus allows for a differential temperature control to enhance or increase exhaust system performance during operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.